Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$123.70	11.617%	$138.0702	$138.07	$138.05	$138.10
Purchase #2	$239.52	4.638%	$250.6289	$250.63	$250.65	$250.60
Purchase #3	$181.27	8.207%	$196.1468	$196.15	$196.15	$196.10
Purchase #4	$174.44	12.573%	$196.3723	$196.37	$196.35	$196.40
Purchase #5	$137.62	7.759%	$148.2979	$148.30	$148.30	$148.30
Purchase #6	$198.41	11.318%	$220.866	$220.87	$220.85	$220.90
Purchase #7	$43.47	4.820%	$45.5653	$45.57	$45.55	$45.60
7 purchase totals =	$1,098.43		$1,195.9474	$1,195.96	$1,195.90	$1,196.00